A portable electronic device operated on a battery of a mobile phone, PHS or PDA as a power supply thereof has conventionally been developed.
A conventional portable electronic device, for example, a mobile phone is powered by a battery and therefore when the battery works out, the device needs to replace it properly or in use of a secondary cell, the device needs to charge the cell, for example, as disclosed in Patent Documents 1 to 3.
However, there occur the following problems that battery replacement accompanies cost and battery replacement or charging needs time and trouble.
As a method for solving such problems, there has been proposed an invention which charges a secondary cell with a solar battery using a light source for backlight and external light, as disclosed in Patent Document 1. However, the invention disclosed in Patent Document 1 uses a light source as only a backlight of a display unit. An electronic device having operation keys illuminates the operation keys using the light source and therefore when the operation keys are illuminated by optical guiding using an optical fiber, the following problem occurs: a structure of the electronic device becomes very complicated.
In addition, the electronic device is configured to charge a solar battery with solar light which has penetrated through the display unit and therefore when the translucency of the display unit is low, the solar battery causes insufficient power generation.
Therefore, a portable electronic device requires a simple structure for good charging as well as extension of a battery drivable period and long lifetime.
In the case of an electronic device having a display element, a light-emitting device is used as a pixel and, in the case of a pixel of a non-light emitting type, a backlight is used, thus causing power consumption for illumination. Therefore, there occurs a serious problem of need for reduction in supply power.
Patent Document 1: Japanese Patent Laid Open Publication No. 2002-77343
Patent Document 2: Japanese Patent Laid Open Publication No. 2001-292214
Patent Document 3: Japanese Patent Laid Open Publication No. 2002-55628